NIPT Formerly Harmony Prenatal Test Dublin*

The testing is non-invasive: it involves taking a blood sample from the mother. The pregnancy is not put at risk of miscarriage, or from other adverse outcomes that are associated with invasive testing procedures such as amniocentesis.

NIPT provides fewer false-positive and false-negative results than combined first trimester screening for trisomy 21, 18 and 13.

It is important to note that NIPT is a screening test and does not provide a definitive genetic diagnosis, as NIPT cannot differentiate potential chromosome differences between the placenta and fetus. A definitive genetic diagnosis of the fetus requires cytogenetic analysis of either amniotic fluid or chorionic villus sampling (CVS).

* Proportion fetuses with trisomy correctly identified by the test as high probability of disorder.

# Proportion of normal fetuses incorrectly identified by the test as high probability of disorder.

NIPT Performance data in a general screening population

NIPT can be ordered by healthcare professionals for women with pregnancies of at least10 weeks’ gestational age. This test can be requested for any singleton or twin pregnancy, including those conceived naturally or by IVF using the patient’s own egg or a donor egg.

Note that, in twin pregnancies, sex chromosome (X and Y) analysis can determine fetal sex but not sex chromosome conditions. This test is not suitable in the case of a vanishing twin. The sex of twins will be reported as one result. If male, one or both of the twins will be male. If female, both twins will be female.

The test does not assess risk for mosaicism, partial trisomies or translocations.

There needs to be enough fetal DNA in the maternal blood to be able to provide a result. If there is insufficient fetal DNA in the sample (which occurs in 2% of cases), another blood sample from the mother may be required. This will be processed in the laboratory at no extra charge.

Once the mother has taken an independent personal decision that she wants to have the NIPT (non-invasive prenatal test) performed, she will be asked to sign a consent form and her blood sample can be taken from a vein in her arm

The mother’s sample and completed request form need to be sent to TDL Genetics, where the test is performed on the DNA extracted from her blood sample.

NIPT does not provide information on mosaicism, partial trisomies or translocations, or other rare chromosomal abnormalities. If the ultrasound scan shows a high nuchal translucency or other major physical defects such as brain abnormalities, heart abnormalities, the risk for some rare chromosomal defects may be high. In such cases, the mother may choose to have a CVS or an amniocentesis.

The non-invasive prenatal test does not provide information on other physical defects such as spina bifida, or information on fetal growth. It is therefore advisable that the mother has all the usual ultrasound scans during her pregnancy.

Trisomy 21 is the most common trisomy, at the time of birth. Also called Down syndrome, it is associated with moderate to severe intellectual disabilities and may also lead to digestive disease, congenital heart defects and other malformations.

Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome) are associated with a high rate of miscarriage. These babies are born with severe brain abnormalities and often have congenital heart defects as well as other birth defects. Most affected individuals die before or soon after birth, and very few survive beyond the first year of life.

The sex chromosomes (X and Y) determine whether we are male or female. X and Y chromosome conditions occur when there is a missing, extra, or incomplete copy of one of the sex chromosomes. The Harmony with X, Y test can assess risk for XXX, XYY, XXYY, XXY (Klinefelter Syndrome), and a missing X chromosome in a girl (Turner Syndrome). There is significant variability in the severity of these conditions, but most individuals have mild, if any, physical or behavioural features.

If the mother is interested in having this optional testing, she should talk with her healthcare provider to determine if it is right for her.

X & Y chromosome conditions are only checked upon request.

On rare occasions, NIPT is unable to provide an assessment of the probability of specific chromosome disorders. This usually reflects the complex biology of genetics and pregnancy, and is not due to a failing in the laboratory.

If NIPT cannot provide a specific assessment, it is not worth repeating the NIPT (unless advised by the laboratory). A decision about other tests (maternal serum screening, detailed ultrasound, amniocentesis or CVS) should be based on the doctor’s assessment of all risk factors identified, and may require specialist consultation.